Posted
by
samzenpus
on Thursday January 10, 2013 @11:06PM
from the acme-approved dept.

An anonymous reader writes "Astronomer and gamer Scott Manley (more famous for his Kerbal Space program coverage) has created a fantastic video explaining the science behind building guns that could one day be used to launch payloads into space. It's not as easy as simply making a bigger gun, there's a whole host of unorthodox 'gun' designs which work around the limitations of garden variety propellants."

Much better than a cannon, and finally a place where we can put all of that electricity from our power plants that we don't use during trough times to be used again when you get a spike. Just gloss over the energy of a small nuclear device in a moving cable over a 2000km area bit. That's not going to bother anyone...

Gerald Bull [www.cbc.ca] solved this problem 20-30 years ago. He even offered it to America, and we told him to kindly go fuck himself, so he did his work in Canada (actually right on the border, with his campus straddling both sides of the border).

Then the Jews decided he didn't deserve to continue living, so they sent a team of assassins to another sovereign country (without permission from that country) to kill him.

If it's acceptable for one country, or two or three, to claim the right of self defense to go after someone who they think might be a threat to them, that country has no right to complain when another country, or group, does the same.

You can't claim you're always being picked on when you're the one doing the bullying.

They were building one aimed at London, but the allies bombed it and it's supply railroad before it was even close to complete.

The allies just got lucky (and had saturated the sky with observation planes) and caught a supply train halfway into the underground supply spur. Didn't know what it was, but dropped a few bunker busters on it just on principle. Also smegged the railroad line.

In a multi-body system there do exist balistic trajectories from one body which do not intersect either body again. However, the moon is too small and too distant to provide the effect from Earth. Conversely, I do believe that such trajectories could exist from the moon.

Generally, the term "mass driver" used to mean electromagnetically accelerated launch systems. Most of these proposals use explosive power. Essentially, this sort of proposal essentially resembles 19th century/early 20th century suggestions for going into space.

Dr. Gerard O'Neill worked on the Mass Driver. (also invented the precursor system to GPS).

He ran up against congressional funding constraints (including one congressman who said that the idea of colonizing space was proof that congress should cut all funding for NASA entirely. This was in the 1980's.)

In the 1970's (and 80's) He sought private funding for development of the Mass Driver - the plan was to install it on the moon, mine materials on the moon, use solar power to electromagnetically launch materia

By any other name the gee force issues are the same. The problem with mass drivers would be the expense. Imagine building a 500 kilometer CERN collider. Mass drivers are practical on the Moon because of the low gravity and no atmosphere.

they have, but it's impractical as in taking up airspace which causes it to act like a wall in the sky preventing airplanes to pass through.it's easier and cheaper to just build a space elevator in the long run.

You mean an electrolysis tank and a power source? Ok, granted there's some engineering to do there but considering the kinds of engineering that would go into building a spacecraft, it's a pretty trivial amount.

You mean an electrolysis tank and a power source? Ok, granted there's some engineering to do there but considering the kinds of engineering that would go into building a spacecraft, it's a pretty trivial amount.

Screw the power source. Panels and reactors are light enough to get up there through traditional means (and with fewer Gs and less chance of damage to them). The water is the heavy part. Just lob tanks of water up there, one after another, and capture them in orbit.

But for what else can you use this gun? We already have plenty of electronic junk up there and it's made its way there just fine without a gun.

Bricks & mortar, figuratively speaking, i.e. batches of construction elements for building structures in space, batches of radiation-shielding materials, in other words anything non-fragile and in bulk.

Major problems included microphonic difficulties and tube failures attributed to vibration and acceleration in gun projectiles. The T-3 fuze had a 52% success against a water target when tested in January, 1942

52% success rate is pretty bad when the bullet is expensive, like many spacecraft are.

These are the same proximity fuzes that kept the acid for the battery that powered them in a glass vial which would shatter on firing, activating the battery just before it was used... right?

Also, I'm pretty sure that they had to use extremely ruggedized tubes - metal housings, and larger internal wires to keep the thing from self destructing or deforming to the point of non-operation. These are

52% is great when your other choice is guessing the distance, and setting a time fuse. The time fuse includes the time you spend loading and firing. Don't drop it.

The proximity fuse had a lot to do with winning the Battle of Britain. The Germans not having the proximity fuse had a lot to do with the success of the bombing of Europe. Too say nothing of their use in the Pacific against the Japanese and again the Japanese not having them to shoot at American bombers.

Why not scale down the LHC and build something that is capable of accelerating something relatively small say 10-100kg fast enough to make it to orbit instead of accelerating atoms to nearly the speed of light.

The problem with conventional rockets is you need to carry the fuel to get in to orbit as well as the fuel to go where you need to. The bigger the ship the more fuel you need to carry to overcome the weight of the fuel.

If you can split the carrying of fuel for your journey from getting your rocket in to orbit you would not need to waste as much fuel lifting itself.

You could set up an automated system that would fire a 10kg payload of fuel every 10 minutes and get what you need over time far cheaper than one big launch.

Orbital speeds in atmosphere means bleeding off speed and part of the payload being vaporized. Its the same forces acting on re-entry. As far as I know (not very far) this makes it harder to send smaller objects.

Orbital speeds in atmosphere means bleeding off speed and part of the payload being vaporized. Its the same forces acting on re-entry.

True. Even worse, you have to start with speed much higher then terminal velocity in the thickest part of atmosphere. Unlike in re-entry, we don't want any atmospheric braking action on the capsule. We would probably have to invent an analogue to supercavitation [wikipedia.org] in air - some means of clearing the path in front and on sides of it.

Why not scale down the LHC and build something that is capable of accelerating something relatively small say 10-100kg fast enough to make it to orbit instead of accelerating atoms to nearly the speed of light.

Accelerating charged particles and accelerating something more complex, like a 10kg payload, are in a completely different ballpark, unless you're happy with send particles into orbit.

Also, each of the protons in the LHC's beam have about as much energy as a fast baseball.

A baseball, per google search, weighs about.142kg and a 120mph baseball is going about 53m/s.

0.5 * mass * velocity^2 gives about 200J.

200J / 1.6e-19 gives around 1.24 x 10^21 eV.

The LHC's protons top out at around 7TeV, or 7 x 10^12.

Your estimate of the LHC's proton energy, sir, is off by a factor of something like 1.78 x 10^8, or in words, by a factor of 178 million, depending on what you think of as a "fast" baseball! (Unless you think of a baseball moving at.009mph as fast?)

It's the g-force involved. The benefit of a long barrel is lower g-forces. A short barrel would be possible but when you start talking a million Gs the only thing that could survive would be solid metals. It's a balancing act of barrel length as opposed to G-Forces involved. There's nothing special about how the LHC is built, magnets or explosives it's still converting energy into motion. Most gun launch systems plan on using explosives to cut costs. Explosives are cheap, magnets and electricity are expensive. If you could do it efficiently one gallon of gasoline would orbit a couple of kilos. The trick is not wasting the energy. As the projectile moves down the barrel the gas expands exhausting it's energy. Say you have a mile long barrel you'd likely run out of gas expansion before you reached the end then add in friction and a projectile that could reach orbit doesn't even make it a mile. Instead burn a cup of vaporized gasoline spaced out every ten feet along the barrel and you might need a few hundred gallons of gas to reach orbit but it's still dirt cheap. Watch the video and he explains why that wouldn't work either. The real solution is lower density gases like hydrogen that have a higher Mach speed. The best bet is watch the video. It's one of the best I've ever seen and explains the problems in laymen's terms.

If you can split the carrying of fuel for your journey from getting your rocket in to orbit you would not need to waste as much fuel lifting itself.

You spend the same amount of energy either way. (Probably more given massive losses to atmospheric drag such schemes suffer from.) TANSTAAFL.

Not that it makes much sense to spend more than the most miniscule of effort to avoid "wasting" fuel. Fuel is cheap, and the cost is all but lost in the noise at current launch costs. (It cost something like a million d

You spend the same amount of energy either way. (Probably more given massive losses to atmospheric drag such schemes suffer from.)

Yes and no. To lift a kg of matter into orbit, and to accelerate it to keep that orbit, you need a certain amount of energy. But this is only a small fraction of the energy an rocket uses [xkcd.com] to do this, because the rocket needs to accelerate all the fuel it is going to use later. So if you could accelrate the rocket before turning it on, you might save quite a lot of fuel.

Why not use a gun to fire fuel to a rocket then?
If you fired the gun every few seconds you wouldn't have the expense of lifting all of the fuel right from the start.
You'd just need the rocket to have some way of catching the fuel. Bit tricky admittedly.

Which part of "it's stupid to spend a lot of money to save fuel because fuel is so cheap" did you fail to comprehend? Pedantic parroting of things you only understand because someone reduced it to your level by producing a cartoon does not contribute usefully to the discussion.

If I understand the math correctly, if the canon can accelerate the rocket to the speed of the exhaust, that would save around 60% of the fuel. Wouldn't that be around on rocket step? And wouldn't leaving one step out save complexitity?

Except - it wouldn't save around 60% of the fuel. A rocket spends much of it's mass lifting it's own mass. A gun spends much of it's energy overcoming atmospheric drag, boosting the shielding needed for that process, and boosting the deadweight of the propulsion system needed to circularize the orbit. It also adds the complexity of splitting the payload down into lots of small chunks and the having to re-assemble those chunks at the far end.

Marianas trench is 11km deep. A neutrally bouyant gun barrel inclined at about 20 gives a barrel length of 30km and is relatively cheap to build (a couple of billion for a few meters diameter).

If you immerse the astronauts in water (body hugging 'bath') they can easily withstand 10-20g for 15-30 seconds. That gives you 2.5-3.5km/s muzzle velocity, and a relatively simple rocket to prvodie the additional 5-6km/s - similar to current rocket second stages.

"Say they could" does not equal "can".
They've got a long way to go before they can prove it.

No they don't. They've already shown they can launch a Dragon, dock it with the ISS, and return safely. The only thing they need to do a manned flight is stick in some seats and an oxygen tank. Granted, it may not be "man rated" yet, but it is not a long way to go.

That's still a very long way from saying "can do it for X million" which is my entire point. There are too many unknowns in the system to be able to put strict dollar estimates down - even the value of the dollar in 2 years plus FFS.

Ah! I thought you were having problems with the time frame, not the price.

Still, $50 million for a SpaceX launch is still a lot closer estimate than being able to build a space gun for a couple of billion dollars. That would take several tens of billions of dollars the way the US government runs things.

This would be ideal for sending inert things like oxygen, water, rocket fuel, or some kinds of food. It would even work for structural parts or electronics if they could take the accelerations without damage.

For that matter, one of the problems of a Mars flight is having adequate shielding against the radiation the craft would encounter between Earth and Mars. With a system like this, the cost of getting the shielding up would be as cheap as possible. (I guess the mass of the shielding would affect the accelerations the craft could make and thus affect the length of the trip.)

One problem, as I understand it: a projectile launched from a big space gun would need to have its orbit adjusted or it will return to Earth. Either you need to catch it while in orbit (you get one chance) and add additional acceleration to put it in a stable orbit, or else the projectile needs to have rockets or something to adjust its speed. The video mentioned this issue briefly (the part about Newton figuring out that the projectile would return to the point of launch if no other forces acted upon it).

P.S. I saw proposals for an Apollo-style mission from Earth to Mars: a single giant rocket launches everything in one launch. Why is anyone even looking at doing it that way? Send the craft to space without fuel or consumables; send it up in parts even and assemble it in space. Then, as it is in orbit, fuel it up, load it with consumables, and then when it is ready send it on its way.

We don't really need giant space guns to make space access more affordable; we just need practical, reusable craft that can carry a small load to orbit, return, and do it again soon. It must not need man-decades of work to completely overhaul it, as the Space Shuttle needed. Single stage to orbit, two stage to orbit, whatever... but not single-use rockets. Rockets that fall into pieces as they ascend, where you never get a test flight because each flight uses up one rocket, will never give us cheap access to space.

According to Jerry Pournelle, the fuel cost of putting something into orbit is similar to the cost of flying it most of the way around the world on an aircraft. Because the aircraft isn't consumed by the flight, we can do this for much less than the cost of sending something into orbit. Practical, reusable transportation would be a total game-changer.

Reusable rockets must be fully overhauled after every single flight and must be more rugged to survive repeated use, they therefore cost more than a disposable rocket. The Saturn 5 was much cheaper than the space shuttle. Using chemical fuels means 95% of the rocket must be fuel. To get usable launch weights you have to use every trick in the book to save weight. All those weight savings make rockets fragile, they wear out quickly and need everything rebuilt after each flight. The only way to make space cheap is by having the power source separate from the rocket/payload (gun, mass driver, loop, skyhook, tractor beam).

One problem, as I understand it: a projectile launched from a big space gun would need to have its orbit adjusted or it will return to Earth. The video mentioned this issue briefly

All gun schemes mention this 'briefly', if they mention it at all (most don't) - mostly in hopes that nobody will notice. The mass of the engines and fuel needed to circularize the orbit dominates the payload, and is *very* difficult to make resistant to the shock and acceleration. It's pretty much a showstopper all by itself, without even mentioning the need for (the currently non-existent) heat shielding needed to protect the payload on ascent. As the vehicle bleeds off energy to atmospheric drag and gravitational forces as it coasts upward, it has to leave the muzzle of the gun at considerably more than orbital velocity... essentialy exposing the payload to re-entry conditions at launch.

P.S. I saw proposals for an Apollo-style mission from Earth to Mars: a single giant rocket launches everything in one launch. Why is anyone even looking at doing it that way?

Nobody that I'm aware that's even remotely serious is proposing to do it that way.

As the vehicle bleeds off energy to atmospheric drag and gravitational forces as it coasts upward, it has to leave the muzzle of the gun at considerably more than orbital velocity... essentialy exposing the payload to re-entry conditions at launch.

The video discusses this point. He really did cover all the bases.

Nobody that I'm aware that's even remotely serious is proposing to do [an Apollo-style mission to Mars]

NASA seems to be at least remotely serious about this mission, an Apollo-style launch. It's n

One problem, as I understand it: a projectile launched from a big space gun would need to have its orbit adjusted or it will return to Earth. The video mentioned this issue briefly

All gun schemes mention this 'briefly', if they mention it at all (most don't) - mostly in hopes that nobody will notice. The mass of the engines and fuel needed to circularize the orbit dominates the payload, and is *very* difficult to make resistant to the shock and acceleration. It's pretty much a showstopper all by itself, without even mentioning the need for (the currently non-existent) heat shielding needed to protect the payload on ascent. As the vehicle bleeds off energy to atmospheric drag and gravitational forces as it coasts upward, it has to leave the muzzle of the gun at considerably more than orbital velocity... essentialy exposing the payload to re-entry conditions at launch.

That's a feature, not a bug. A layer of heat shielding would cover the nose of the projectile, allowing it to survive ascent. During ascent, however, the shield would be ablated. If the projectile is not captured before it deorbits, it vaporizes on reentry.

After the construction of the gun, each launch is relatively cheap. The high G forces experienced by the payload would exclude using a gun for fragile materials. It's a perfect system for putting lots of dead mass into orbit cheaply, though (water, soil,

The necessity of momentum to circularize the orbit is clear if your model consists of only the Earth and the satellite, but I wonder if the gravitational pull of the moon could be used.What if we could shoot something up to a Lagrange point? Would we still need engines in our satellite?

You can always find somebody proposing some damm fool hare brained scheme or another. Finding someone to actually *pay* for it, is however another matter entirely.

The key issue with a gun is that it's a very expensive and risky solution wandering about in search of a problem. The folks with the bucks know this. The dreamers, since they aren't required to be grounded in the real world, don't.

The high velocity at the muzzle is an advantage if you add a scram jet to the launch vehicle.

Only if you've screwed something up very, very badly in your design and end up with muzzle velocity far below anything useful. Otherwise, you transit the atmosphere too fast for scramjets to be anything but dead weight. Even assuming you can get the scramjet to function in what are essentially re-entry conditions (a huge assumption at best) their weight far exceeds any useful performance.

An issue with reusable launch vehicles is that, due to the stresses of launch, parts have a tendency to bend and break. It can be quite difficult to find and diagnose these issues. Things can even become fuses and need to be replaced. It is quite similar to a drag racer. After each run the entire engine is re-built and they don't last many runs. One can build an item much lighter if it is tuned to almost destroy itself while doing it's job. A single use rocket has to hold itself together just long enough to

At those speeds you need the barrel, track, or rail straight to extreme precision. Any deviations will set up a wave in the track that will destroy it.We built a 1000 ft light gas gun and had it happen. A couple hundred feet down the track the projectile existed through the wall of the tube and the tube was bent into a sin wave.

"At a meeting of astronomers, their president proposes a trip to the Moon. After addressing some dissent, six brave astronomers agree to the plan. They build a space capsule in the shape of a bullet, and a huge cannon to shoot it into space."

As in a "gun" (weapon) used in space, which is to me a MUCH more fascinating engineering and design problem. In space, inertia and recoil are a bitch.

Missles probably impractical because they rely on aerodynamic forces to steer (nozzle alone isnt enough to change course/ uses too much fuel), whch leaves us energy and projectile weapons. Turrets can't whip around. Anything kinetic needs to dissipate the recoil which will favor recoilless designs, but those have their own complexities (current designs still h

As in a "gun" (weapon) used in space, which is to me a MUCH more fascinating engineering and design problem. In space, inertia and recoil are a bitch.

Missles probably impractical because they rely on aerodynamic forces to steer (nozzle alone isnt enough to change course/ uses too much fuel), whch leaves us energy and projectile weapons. Turrets can't whip around. Anything kinetic needs to dissipate the recoil which will favor recoilless designs, but those have their own complexities (current designs still have -some- recoil, which while negligible on the surface would have a magnified effect in space). the classic problem of what to do with the heat buildup.

I honestly think space combat will favor a design that is the fusion of two "obsolete" technologies, that of battleship and bomber, though i'm thinking more medium/dive attac bomber. the battleship classic standard is that of dishing and taking damage; this translates to a large mass, and more mass has advantages for absorbing both recoil and heat. the bomber side from the concept of lobbing essentially dumb munitions (bombs or "depth" charges) on a calculated physics trajectory. Though the trouble there, is there no fluid medium to tranfer the energy, so the munition either absolutely must impact the target directly, or cast out a large amount of shrapnel (which would complicate the battlefield for the attacker too).

http://www.youtube.com/watch?v=QShvDj12xBc [youtube.com]
"This is the concept for a 10,000 Meter ( 30,000 Foot), ballon-supported space gun.
The tube or barrel is 0.6 Meters (2 feet) in diameter, so it is intended for launching very small payloads.
It is unknown how plausable this is,.

The goal is to get above 10K meters, as the atmosphere is less than 50% as dense as sea level, thus friction should be low and momentum from accelleration up the tube or barrel should encounter less resistance."

Dr. James Powell, co-inventor of superconducting Magnetic Levitation (MagLev), is also a co-inventor of a system called StarTram, that uses similar electromagnetic technology to launch manned and unmanned vehicles into space.